Wearable devices are provided including electrical contacts to detect voltages or other biosignals when mounted to the skin of a wearer. The impedance between a pair of the electrical contacts can be detected and the device operated based on the detected impedance. The device can detect an electrocardiogram or other biopotentials using the electrical contacts if the detected impedance falls below a specified threshold. The device could indicate that the detected impedance is below the specified threshold, e.g., such that a wearer could contact one of the electrical contacts with a finger to allow detection of an electrocardiogram between the arms of the wearer. The device could indicate that the detected impedance remains greater than the specified threshold, e.g., such that a wearer could re-mount the wearable device to improve the electrical connection between the electrical contacts and the wearers skin.
